Geophysical surveys are often used for oil and gas exploration in geophysical formations, which may be located below marine environments. Various types of signal sources and geophysical sensors may be used in different types of geophysical surveys. Electromagnetic (EM) surveys, for example, may be conducted using EM signals transmitted by an EM source and detected by EM sensors. Seismic geophysical surveys, for example, are based on the use of acoustic waves. In seismic surveys, a survey vessel may tow an acoustic source (e.g., an air gun or a marine vibrator) and a plurality of streamers along which a number of acoustic sensors (e.g., hydrophones and/or geophones) are located. Acoustic waves generated by the source may then be transmitted to the earth's crust and then reflected back and captured at the geophysical sensors. Data collected during a marine geophysical survey may be analyzed to locate hydrocarbon-bearing geological structures, and thus determine where deposits of oil and natural gas may be located.
During a seismic survey, up-going wavefields may reflect from the water surface, resulting in down-going ghost signals that may be detected by geophysical sensors along with desired up-going wavefields from the formation. Ghost signals may attenuate the up-going wavefield and cause notches in measured signals at particular frequencies. Reduction or elimination of these notches may improve survey resolution.